Okay, so I saw this earlier and just got home to type this. I'm using Steam Market just b/c third party marketplaces can shaft you and the M9 example is in abundance so the price is fairly true. I'm also measuring in USD b/c I'm not a 3rd world bottom-feeder. I did a bit of math using Talon Knife prices and M9 prices. I used the M9 as a sample to see the multiplier from Phase 2 price to Ruby price. The median price of a M9 Doppler Phase 2 is about $315 and the median Ruby price is about $1,715. That is a multiplier value of 5.44x. Now a standard Talon Knife Phase 2 is $725 on the market. B/c the knife is somewhat new they're not in abundance. But using the price of $725 and the multiplier of 5.44x you get $3,944. But the problem with this price, is the rarity of the knife and the decent float. I have yet to see the knife you described anywhere, so the math doesn't necessarily hold up. 4 Gs for that knife would be a reasonable amount for me, but it's definitely worth more.